1. Field of the Invention
The present invention relates to a light-emitting semiconductor device having a substrate, on which multiple semiconductor layers made of group III nitride group compound semiconductor may be laminated.
2. Description of the Related Art
FIG. 8 illustrates a sectional view of a conventional semiconductor layer 900 made of group III nitride group compound. As shown in FIG. 8, the semiconductor layer 900 has a multiple quantum well structure.
In a conventional light-emitting device using group III nitride group compound semiconductor, e.g., LD and LED, quantum well layers qwn (n=1, 2) formed in the multiple quantum well 900 are made of gallium indium nitride (Ga1-xbInxbN; 0.10<xb<0.25) and quantum barrier layers qbm (m=1, 2, 3) are made of gallium nitride (GaN).
Especially, in order to form a blue-light-emitting quantum well layer, composition ratio x of indium is preferably around 0.15.
Upper limits of n and m are arbitrary. When the upper limit of n is 1, the light-emitting device using group III nitride group compound semiconductor, e.g., LD and LED, has a single quantum well (SQW) structure.
However, the following problems persist in the conventional light-emitting semiconductor device.
Problem 1: While a quantum well layer qwn is growing, spatial deviation (spatial deviation of existence density) of InN compositions in a quantum well layer tends to occur. Because of this non-uniformity of compositions, light which has colors of high purity and narrow half-width in an emission spectrum cannot be obtained.
Problem 2: By cooling after crystal growth of the semiconductor layer, heat-shrinkage may occur in the light-emitting device that causes warpage and stress to remain in the device. Because a conventional light-emitting device (an active layer) may be affected by residual stress, the device cannot sufficiently control the driving voltage (oscillation threshold). Additionally, because of such stress and high driving voltage, the performance life of the device decreases.
Problem 3: Especially, when a quantum well layer having a thickness less than 50 nm is laminated in a light-emitting device (an active layer), the quantum well layer, which is relatively thin, may become easily affected by the internal stress. As a result, especially when such a thin quantum well layer is laminated in the light-emitting device (an active layer), internal stress tends to become a significant problem.